Hitherto, various techniques have been proposed for provision of a disposable sheet material capable of being washed away in a flush toilet, more specifically a water-disintegrable paper of the type which includes a soft-wood pulp mass and a water-soluble binder (CMC, PVA or the like) with which the constituent parts of the wood pulp mass are bound together (as described in Japanese Patent Application Laid-Open Publication Nos. 2-154095, 2-229295, and 3-167400). Also, a number of disclosures have been made with respect to wipes using such a sheet material, as described in Japanese Patent Application Laid-Open Nos. 2-149237, 3-182218, and 3-292924.
With such water-disintegrable paper and wipes using such a paper material it is expected that they, after having been flushed away with water in a flush toilet, can be biologically treated to a satisfactory extent in a septic tank and/or in a sewage disposal plant, because their main component material is a soft-wood pulp. However, a sheet comprised chiefly of a soft-wood pulp is a material known commonly as paper and is not softer than a nonwoven fabric formed from a synthetic fiber material. Therefore, the sheet feels less comfortable to the hand or skin. Although the sheet possesses good hydrophilic and water absorption properties, it has disadvantages that in its wet condition the sheet tends to collapse as its fiber components lose their impact resilience, being thus liable to feel sticky to the skin, and that in such a condition the sheet tends to be adversely affected in respect of softness, an essential feature required of wipes.
Whilst, it is widely known to use a wet-laid nonwoven fabric containing a synthetic fiber material (such as PE (polyethylene), PP(polypropylene), or PET (polyethyleneterepythalate)) to provide non-water-disposable wipes. When used in applications such as wipes and sanitary materials, a nonwoven fabric comprising such a synthetic fiber feels softer than paper and exhibits more comfortable hand. However, the trouble with such a material is that the material is non-biodegradable in a septic tank and/or in a sewage disposal plant. This fact leads to an important problem such as a noticeable increase in the volume of solid residues.
As such, recently, a water-disposable sheet including a biodegradable fiber material has been proposed as described in Japanese Patent Application Laid-Open No. 7-70896. However, the teaching of the JP Laid-Open No. 7-70896 is such that the sheet is comprised merely of a biodegradable synthetic fiber and a binder and, therefore, does not meet the need for a sheet capable of sufficient absorption of an impregnating solution thereinto as required for fabrication of a wet wiper. In addition, the sheet has much poorer tensile strength as compared with conventional sheets of the type comprised of a pulp component and a binder, which means that a product using the sheet is of insufficient strength.